How to seam these holes in my object?
Your mesh is a bit messy, you have floating edge along its axis, you can see if you hide some faces:

What you could do to fix it quickly is enabling the Affect Only Origins option:

Move the origin very slightly to the right:

Disable the option, then back in Edit mode, select all, go in the Mesh menu &gt; Symmetrize:

In the Operator box choose the right axis (in your case +Y to -y)

Your mesh has been symmetrized and the floating edges has been deleted in the process.